1990 Spark plugs - ZR-1 Net Registry Forums

SteveCanyon · 04-30-2015

I did a search for spark plugs but guess I did not find what I was looking for. What plugs are people using in their 1990? I don't want to use any of the plugs that I have to over torque. Autozone, O'Reilly's, etc, give a long list of plugs that match. I do prefer an iridium plug.

Paul Workman · 05-01-2015

AC Delco #41 602s work very well in several stock and modified cars. You can pay way more, but these will work well and are cheap enough you can replace them long before they're used up: always have a fresh set, doancha know.

The 90 head spark plug wells are cut with flat bottoms so whatever plug you end up with be sure they cross-reference to these AC plugs and have the ring seal (washer) attached.

efnfast · 05-01-2015

I hope Marc doesn't mind me quoting him. - In an e-mail he sent me.

"For high load operation I recommend a spark plug that is one AC heat range cooler than the OE plug. The best spark plug is the NGK TR7IX. Part number 3690.

It has a tapered seat. All LT5's are machined for both tapered and flat seat plugs. Carefully open the gap to .050"

Best of luck.

Marc"

Vette73 · 05-02-2015

I to are probably going to change my plugs soon or at least pull them and see what color they are....Car runs great with no issues 'so far'...

Just did headers,exhaust,chip and intake temp relocation wire.....

Am i good with the plugs Marc suggested in the previous post? What about gap? 50?

Thanks......

Hib Halverson · 05-03-2015

As is often the case, Marc H. is right about the proper heat range for the LT5 plug.

Just before the cars went on sale in 1990, GM changed the spark plug recomendation from the FR-1LS to the FR-2LS. The reason for this was concern on the part of the dealer network about "pre-delivery fouling". What this means is the AC "1" heat range really is the proper type of plug to run as long as the engine doesn't see a lot of duty where it is started, run at idle and low speed for a very short period then shut off.

Needless to say, the AC 2 heat range is too hot a plug for most LT5s. The AC 1 heat range is equivalent to the NGK 6 and the Denso 20 heat ranges and that should be the hotest plug anyone should consider unless the most you ever run your LT5 is a few minutes.

I've run the Denso IT-22 (crosses to the NGK TR7IX) in my LT5 for a number of years. It's a great street performance spark plug. The IT-22 uses a very fine, iridum center electrode and a u-groove ground electrode.

As for running taper seat plugs in heads which have previously used only flat set plugs, to convert to the taper seat, the first time you install taper seat plugs you have to torque them to 22-ft/lbs to form the taper seat. Then loosen the plug and re-torque it to 15 lbs/ft

SteveCanyon · 05-03-2015

I asked Mark about a plug with the flat washer and he said a good choice is the AC Delco 41-800 gapped at .050 so may give those a try.

bradley · 05-04-2015

I am a poor guy I run 3923 autolites , and gap them @40 thou as I have the cometic head gaskets on my car after the rebuild and compression is now 11.4. no the car doesn't get a rash form the autolites .lol

04-30-2015	#1
SteveCanyon Join Date: Apr 2015 Location: Northwest AR Posts: 95	1990 Spark plugs I did a search for spark plugs but guess I did not find what I was looking for. What plugs are people using in their 1990? I don't want to use any of the plugs that I have to over torque. Autozone, O'Reilly's, etc, give a long list of plugs that match. I do prefer an iridium plug. Last edited by SteveCanyon; 04-30-2015 at 10:29 PM.

05-01-2015	#2
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: 1990 Spark plugs AC Delco #41 602s work very well in several stock and modified cars. You can pay way more, but these will work well and are cheap enough you can replace them long before they're used up: always have a fresh set, doancha know. The 90 head spark plug wells are cut with flat bottoms so whatever plug you end up with be sure they cross-reference to these AC plugs and have the ring seal (washer) attached. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry Last edited by Paul Workman; 05-01-2015 at 11:42 AM.

05-01-2015	#3
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,237	Re: 1990 Spark plugs I hope Marc doesn't mind me quoting him. - In an e-mail he sent me. "For high load operation I recommend a spark plug that is one AC heat range cooler than the OE plug. The best spark plug is the NGK TR7IX. Part number 3690. It has a tapered seat. All LT5's are machined for both tapered and flat seat plugs. Carefully open the gap to .050" Best of luck. Marc"

05-03-2015	#5
Hib Halverson Join Date: Jun 2005 Location: CenCoast California Posts: 899	Re: 1990 Spark plugs As is often the case, Marc H. is right about the proper heat range for the LT5 plug. Just before the cars went on sale in 1990, GM changed the spark plug recomendation from the FR-1LS to the FR-2LS. The reason for this was concern on the part of the dealer network about "pre-delivery fouling". What this means is the AC "1" heat range really is the proper type of plug to run as long as the engine doesn't see a lot of duty where it is started, run at idle and low speed for a very short period then shut off. Needless to say, the AC 2 heat range is too hot a plug for most LT5s. The AC 1 heat range is equivalent to the NGK 6 and the Denso 20 heat ranges and that should be the hotest plug anyone should consider unless the most you ever run your LT5 is a few minutes. I've run the Denso IT-22 (crosses to the NGK TR7IX) in my LT5 for a number of years. It's a great street performance spark plug. The IT-22 uses a very fine, iridum center electrode and a u-groove ground electrode. As for running taper seat plugs in heads which have previously used only flat set plugs, to convert to the taper seat, the first time you install taper seat plugs you have to torque them to 22-ft/lbs to form the taper seat. Then loosen the plug and re-torque it to 15 lbs/ft __________________ Hib Halverson Technical Writer former owner 95 VIN 0140 current owner 19 VIN 1878 Last edited by Hib Halverson; 05-03-2015 at 10:21 PM.

05-03-2015	#6
SteveCanyon Join Date: Apr 2015 Location: Northwest AR Posts: 95	Re: 1990 Spark plugs I asked Mark about a plug with the flat washer and he said a good choice is the AC Delco 41-800 gapped at .050 so may give those a try.

05-02-2015	#4
Vette73 Join Date: Nov 2014 Location: Brooklyn ny Posts: 1,045	Re: 1990 Spark plugs I to are probably going to change my plugs soon or at least pull them and see what color they are....Car runs great with no issues 'so far'... Just did headers,exhaust,chip and intake temp relocation wire..... Am i good with the plugs Marc suggested in the previous post? What about gap? 50? Thanks......

05-04-2015	#7
bradley Join Date: Aug 2013 Location: ridgecrest ca Posts: 104	Re: 1990 Spark plugs I am a poor guy I run 3923 autolites , and gap them @40 thou as I have the cometic head gaskets on my car after the rebuild and compression is now 11.4. no the car doesn't get a rash form the autolites .lol